In a rotating electric machine functioning as a motor, or a generator or a motor/generator, it is preferred that the stator core and the rotor are cooled in order prevent generation of heat.
Tokkai Hei 5-236705 published by the Japanese Patent Office in 1992, Tokkai Hei 7-322565 published by the Japanese Patent Office in 1995 and Tokkai Hei 11-69721 published by the Japanese Patent Office in 1999 disclose a rotating electric machine provided with a passage for a cooling medium in a stator core.
The cooling of the stator core allows the indirect cooling of the rotor. Therefore when the stator core is sufficiently cooled, it is not necessary to provide a cooling structure for the rotor. However when a passage for the cooling medium is formed in the stator core, it is sometimes the case that the passage for the cooling medium hinders the flow of magnetic flux and reduces the output of the rotating electric machine. In the prior-art techniques referred to above, the passage for the cooling medium is disposed without taking into account any adverse effect the passage for cooling medium may have on the flow of magnetic flux.
On the other hand, Tokkai Hei 4-364343 published by the Japanese Patent Office in 1992 discloses a cooling structure using a space in a slot as a passage for a cooling medium such as oil. The passage for cooling medium is formed by sealing the opening of a stator slot with a resin layer. In this manner, the flow of magnetic flux is not impeded by the passage for the cooling medium in contrast to forming the passage for the cooling medium in the stator core. Consequently there is no reduction in the output of the rotating electric machine. However in this type of cooling structure, since the coils are wound on the teeth of the stator core, the area of contact of the cooling medium with the stator core is small and the cooling passage is not provided in direct contact with the stator core. Therefore it is difficult for this type of cooling structure to realize sufficient reductions in the temperature of the stator core.